Stable lead alkyl compositions and a method for preparing the same



United States Patent Oiiice 3,133,098 Patented May 12, was

. 3,133,0fi8 STABLE LEAD ALKYL QUMPOSITIGNS A METHOD EUR PREPARING THE SAME Shirl E. Cook and Wilford H. Thomas, Baton Rouge, La., assignors to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed June 8, 1962, Ser. No. 200,933 1%) Claims. (Cl. 260-437) This invention relates to alkyllead compositions which are stable at temperatures above 100 C. It also relates to methods for inhibiting the thermal decomposition of alkyllead compounds when subjected to temperatures above 100 C., at which temperature thermal decomposition becomes appreciable.

Generally this invention contemplates inhibiting the thermal decomposition of alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical.

More specifically, this invention is concernedwith an improved process for separating alkyllead compounds from the reaction products accompanying their synthesis. It is also applicable to a method for inhibiting thermal decomposition of an alkyllead product during its purification and blending with other products in making commercial antiknock fluids. It is applicable to minimizing the possibility of thermal decomposition during storage or transportation of an alkyllead product. It is especially applicable to preventing thermal decomposition of undiluted alkyllead compounds where the likelihood of thermal decomposition is more of a problem.

As is well known, tetraalkyllead antiknock compounds generally are produced by reacting a sodium-lead alloy with an alkyl halide. Due to recent marked improvements in the technology of alkyllead manufacture, thermal instability of alkyllead compounds during synthesis is no longer a problem. However, the tetraalkyllead compound so produced is in admixture with various reaction by-products from which it must be separated. Separation is effected by steam or vacuum distillation with subsequent purification of the tetraalkyllead distillate. Due to the toxic and unstable nature of tetraalkyllead antiknock compounds, these distillation and purification operations are subject to many difliculties.

In these distillation and purification operations meticulous temperature control and exact safety measures are of paramount importance. The rate of decomposition of the alkyllead compound increases rapidly with small rises in temperature above the temperature where thermal decomposition becomes appreciabie. For example, decomposition of tetraethyllead occurs at the rate of approximately 2 percent per hour at a temperature of 100 C., which is the customary temperature used in separating tetraethyllead from the reaction products accompanying its synthesis. At temperatures above 100 C., the decomposition rate increases logarithmically so that a point is soon reached where external heat is no longer required and decomposition becomes selfpropagating.

Such likelihood of excessive decomposition is present also during blending, handling, storage, and transportation. Prior to diluting the alkyllead concentrate with scavengers, gasoline or other materials, the alkyllead compound remains a concentrate and the problem of excessive thermal decomposition exists, even though the temperature is maintained normally well below that of decomposition. For example, in the purification step wherein the tetraethyllead concentrate is washed and blown with air at atmospheric temperature to remove impurities, a sudden increase in temperature may occur due to the oxidation of triethylbismuth which is present as an impurity. Also pumps used in handling tetraethyllead ocmerce.

casionally freeze and the friction developed may cause a local overheating to a temperature above the temperature of decomposition of the tetraethyllead. Faulty wiring, leaks onto steam pipes, and other accidental causes also may produce local overheating with resulting dangerous decomposition.

It is seen therefore that in those operations where an alkyllead compound is in the undiluted or concentrated state-viz. separation, purification, blending, transportation, and storage-the likelihood of excessive thermal decompositionmust be provided for and effectively combatted.

An object of this invention is to stabilize alkyllead compounds against thermal decomposition during one or more of the following operations: separation, purification, blending, transportation and storage.

The above and other objects of this invention are accomplished byincorporating with alkyllead compounds a relatively small quantity of a material having the property of inhibiting alkyllead thermal decomposition. The foregoing objects are also accomplished by conducting one or more of the foregoing operations in the presence of such a material. The materials which have been found to possess these unexpected properties are referred to hereinafter as thermal stabilizers.

The thermal stabilizer of this invention is tall oil. It has been found that this material very effectively inhibits the thermal decomposition of alkyllead compounds even when this is the sole additive associated with the alkyllead compounds. For this purpose tall oil concentrations ranging from about 0.5 to about 30 percent or more based on the weightof the alkyllead give very satisfactory results. Generally speaking the preferred concentrations of tall oil range from about 2 to about 20 percent based on the weight of the alkyllead compound being stabilized.

It has been further found that tall oil when used in conjunction with ethylene dibromide gives rise to a synergistic inhibition of alkyllead thermal decomposition. Thus a preferred embodiment of this invention involves the utilization of mixtures of ethylene dibromide and tall bil, the concentration of the ethylene dibromide being equivalent to from about 0.05 to about 0.5 mole per mole of alkyllead compound, the concentration of the tall oil rang ing from about 0.5 to about 30 percent by weight based on the weight of the alkyllea-d compound. Here again the preferred tall oil concentration range is from about 2 to about 20 percent by weight based on the weight of the alkyllead compound. Thismixture of thermal stabilizers when .used in the foregoing amounts is particularly effective in substantially retarding or preventing thermal decomposition of the alkyllead compounds at temperatures ranging from about C. up to C. for extended periods of time.

The identity and chemical makeup of tall oil is of course well known to those skilled in the art. (Reference may be had, for example, to The Merck Index, 7th edition,Merck and Co., -Inc., Rahway, New Jersey, 1960.) The material is normally derived as a by-product of the wood pulp industry and is sometimes referred to as liquid rosin. A feature of this invention is that tall oil is available from a number of commercial suppliers at low cost. Thus the discovery of the effectiveness of this material in accordance with this invention makes possible the use of a plentiful, readily available, low cost commodity of com- Although the chemical composition of tall oil is generally uniform there is some variation from supplier to supplier and some variation from grade to grade of material. Nonetheless all of the commercially available tall oils are useful in the practice of this invention.

The chief thermal decomposition products of alkyllead compounds are lead metal and hydrocarbon gas. Hence,

a very good index of alkyllead thermal decomposition is liberation of this gas.

T illustrate the effectiveness of this invention, a series of direct comparisons were made of the decomposition characteristics of unstabilized and stabilized tetraethyllead samples. A thermostatically controlled hot oil bath was fitted with a stirrer, thermometer, and a'holder for a small reaction tube. A 100 cc. gas buret beside the bath, and equipped with a water-containing levelling bottle, was connected by means of rubber tubing with the reaction tube after the desired sample was introduced into this tube. After the bath was brought to a steady temperature of 195 C., the sample-containing tube was quickly immersed in the bath and clamped with the levelling bottle adjusted to hold the gas buret in place at a zero reading. Then measured was the time during which the sample was held at 195 C. without pronounced thermal decomposition and consequent gas evolution occurring. Thus, the longer the time, the more thermally stable was the alkyllead composition.

With pure tetraethyllead used in 1 ml. amounts, pronounced thermal deterioration occurred almost immediately as evidenced by rapid gas evolution. In fact, the decomposition of unstabilized tetraethyllead will normally become uncontrollable if it is heated, whether rapidly or slowly, to even 130 C., unless it is possible to very rapidly cool it down to about 100 C. or below.

The remainder of the compositions tested in the manner described above and the results thereby obtained are shown in the following table.

TABLE Efiect of Additives on Thermal Decomposition of Alkyllead Compounds at 195 C.

The tall oil utilized in runs 1 and 2 above was an article of commerce, the manufacturers specifications of which called for a titer of 24 C., a density figure of 7.51-7.59 pounds per gallon at 25 C., an acid number of 0.80- 0.85, and a saponiiication number of 183-188. It will be seen that this typical tall oil was very eifective when utilized by itself as an additive (run 1) and that it cooperated with the ethylene dibromide to exert a very substantial synergistic efiect (run 2). Such results are typical of the results achieved using any commercially available tall oil composition.

The above-described beneficial behavior of the thermal stabilizers of this invention also takes place with other alkyllead compounds such as triethyllead bromide and tetrapropyllead. In fact, these compounds when stabilized can be boiled and distilled at atmospheric pressure.

This invention is adapted to the stabilization of tetraethyllead and other alkyllead compounds at various stages after they have been formed and the diluents or excess allcyl halide have been discharged from the autoclave. For example, one of the above thermal stabilizers may be added in appropriate quantity to the alkyllead reaction concentrate just before the separation step which is conducted at a temperature close to the temperature 4 where hazardous run-away decomposition is particularly prevalent. By adding one of the above thermal stabilizers to the reaction concentrate just prior to distillation, the danger arising from unexpected temperature increases is substantially eliminated.

Most preferably the above thermal stabilizers are employed to stabilize the alkyllead compound both in storage and in shipping and especially to stabilize any alkyllead concentrate, i.e., compositions containing at least percent by weight of alkyllead compound. If elevated temperature conditions are likely to be encountered, the addition of a small amount of thermal stabilizer to the alkyllead compound will economically and satisfactorily eliminate most of the hazard involved. While meticulous temperature control and exacting safety measures have been successful in reducing to a minimum the hazards of processing and handling of tetraethyllead, the use of this invention provides a much greater factor of safety. Furthermore, waste of the alkyllead product due to decomposition is considerably minimized through the use of this invention.

This invention is useful in stabilizing alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical. For example tetraethyllead, tetramethyllead, tetrapropyllead, dimethyldiethyllead, triethylphenyllead, and triethyllead bromide can be successfully stabilized against thermal decomposition by incorporating therein a relatively small quantity of one of the thermal stabilizers of this invention. This invention is particularly well suited to the stabilization of any mixture involving two or more of the following compounds: tetramethyllead, ethyltrimethyllead, diethyldimethyllead, triethylrnethyllead, and tetraethyllead.

What is claimed is:

1. A method of inhibiting the decomposition of a concentrated allryllead compound at temperatures of from about C. to about C. which comprises incorporating with said compound from about 0.5 to about 30 percent of tall oil based on the weight of said compound.

2. A method of inhibiting the decomposition of a concentrated alkyllead compound at temperatures of from about 100 C. to about 195 C. which comprises incorporating with said compound from about 0.05 to about 0.5 mole of ethylene dibromide per mole of said compound, and from about 0.5 to about 30 weight percent of tall oil based on the weight of said alkyllead compound.

3. In the process of producing an alkyllead compound by reacting a sodium lead alloy with alkyl chloride and separating the thus produced alkyllead compound from the reaction mass by steam distillation, the step which comprises conducting said steam distillation in the presence of from about 0.5 to about 30 weight percent of tall oil based on the weight of said compound.

4. in the process of producing an alkyllead compound by reacting a sodium lead alloy with alkyl chloride and separating the thus produced alkyllead compound from the reaction mass by steam distillation, the step which comprises conducting said steam distillation in the presence of from about 0.05 to about 0.5 mole of ethylene dibromide per mole of said compound, and from about 0.5 to about 30 weight percent of tall oil based on the weight of said alkyllead compound.

5. A concentrated alkyllead compound with which has been blended from about 0.5 to about 30 weight percent of tall oil based on the weight of said compound.

6. The composition of claim 5 wherein the concentration of the tall oil is from about 2 to about 20 weight 7 percent based on the weight of said compound.

7. A concentrated alkyllead compound with which has been blended from about 0.05 to about 0.5 mole of ethylene dibromide per mole ofrsaid compound, and from about 0.5 to about 30 weight percent of tall oil based on the weight of said alkyllead compound.

8. The composition of claim 7 wherein the concentrationof the tall oil is from about 2 to about 20 weight 3,133,098 5 6 percent based on the weight of said alkyllead compound. yllead, ethyltrimethyllead, diethyldimethyllead, ttiethyl- 9. The composition of claim 5 wherein said compound methyllead, tetraethyllead, and mixtures thereof. is selected from the group consisting of tetramethyllead,

ethyltrimethyllead, diethyldimethyllead, triethylmethyl- References Clted m the file of thls patent lead, tetraethyllead, and mixtures thereof. 5 UNITED STATES PA NTS 10. The composition of claim 7 wherein said com- 2,686,713 White et a1 Aug. 17, 1954 pound is selected from the group consisting of tetrameth- 3,015,547' Heisler et a1. Jan. 2, 1962 

1. A METHOD OF INHIBITING THE DECOMPOSITION OF A CONCENTRATED ALKYLLEAD COMPOUND AT TEMPERATURES OF FROM ABOUT 100*C. TO ABOUT 195*C. WHICH COMPRISES INCORPORATING WITH SAID COMPOUND ABOUT 0.5 TO ABOUT 30 PERCENT OF TALL OIL BASED ON THE WEIGHT OF THE COMPOUND. 